WASHINGTON — Defense Secretary Leon Panetta is lifting the military's ban on women in combat, which will open up hundreds of thousands of additional front-line jobs to them, senior defense officials said Wednesday.

The groundbreaking decision overturns a 1994 Pentagon rule that restricts women from artillery, armor, infantry and other such combat roles, even though in reality women have found themselves in combat in Iraq and Afghanistan, where more than 20,000 have served. As of last year, more than 800 women had been wounded in the two wars and more than 130 had died.

Defense officials offered few details about Panetta's decision but described it as the beginning of a process to allow the branches of the military to put it into effect. Defense officials said Panetta had made the decision on the recommendation of the Joint Chiefs of Staff.

Women have long chafed under the combat restrictions and have increasingly pressured the Pentagon to catch up with the reality on the battlefield. The move comes as Panetta is about to step down from his post and would leave him with a substantial legacy after only 18 months in the job.

Panetta's decision came after he received a Jan. 9 letter from Gen. Martin E. Dempsey, the chairman of the Joint Chiefs of Staff, who stated in strong terms that the armed service chiefs all agreed that "the time has come to rescind the direct combat exclusion rule for women and to eliminate all unnecessary gender-based barriers to service."

But there was a note of caution. "To implement these initiatives successfully and without sacrificing our war fighting capability or the trust of the American people, we will need time to get it right," Dempsey wrote.

A copy of Dempsey's letter was provided by a Pentagon official under the condition of anonymity.

The letter noted that this action was meant to ensure that women as well as men "are given the opportunity to succeed."

As recently as two months ago, four servicewomen filed a federal lawsuit against the Pentagon challenging its combat restriction, saying they had all served in combat in Iraq or Afghanistan but had not been officially recognized for it. One of the women, Maj. Mary Jennings Hegar, an Air National Guard helicopter pilot, was shot down, returned fire and was wounded while on the ground in Afghanistan, but said she could not seek combat leadership positions because the Defense Department did not officially acknowledge her experience as combat.

In the military, serving in combat positions like the infantry remains crucial to career advancement in the military, and women have long said that by not recognizing their real service the military has unfairly held them back.

It is unclear to what degree Congress will review the decision, although in the past some Republican members of the House have balked at allowing women in combat. In recent years they have asked the Pentagon sometimes sharp questions when it became clear from news reports that women were in fact serving in combat in Iraq and Afghanistan.

But as of Wednesday afternoon, there appeared to be bipartisan support for the decision on Capitol Hill.

Sen. Patty Murray, D-Wash., the chairwoman of the Senate Veterans' Affairs Committee, called it a "historic step for recognizing the role women have, and will continue to play, in the defense of our nation." She added that "in recent wars that lacked any true front lines, thousands of women already spent their days in combat situations serving side-by-side with their fellow male service members."

Sen. Kelly Ayotte, R-N.H., a member of the Armed Services Committee, said in a statement that she was pleased by the decision and that it "reflects the increasing role that female service members play in securing our country."

In his letter, Dempsey said that work remained to set the proper performance standards, both physical and mental, for the new military roles now opening to women. He also set a number of "goals and milestones," with quarterly progress updates required from the services.

In particular, the Navy will continue to assign more women to warships as privacy and berthing changes are completed.